Saturday, 4 October 2008

News Round

Use it or lose it? Researchers investigate the dispensability of our DNA

Our genome contains many genes encoding proteins that are similar to those of other organisms, suggesting evolutionary relationships; however, protein-coding genes account for only a small fraction the genome, and there are many other DNA sequences that are conserved across species. What are these sequences doing, and do we really need them at all? In a study published online today in Genome Research, researchers have delved into this mystery and found that evolution has actively kept them in our genome.

Before the human genome was sequenced, researchers estimated the genome might contain upwards of 140,000 protein-coding genes, but surprisingly, sequencing revealed only about 20,000, accounting for less than 2% of the entire genome. Previously, Dr. Gill Bejerano of Stanford University found that lurking within the other 98% of the genome are stretches of sequences, known as ultraconserved elements, which are identical between humans and animals such as rodents and chickens, even though hundreds of millions of years of independent evolution separates them.

MicroRNAs, the tiny molecules that fine-tune gene expression, were first discovered in 1993. But it turns out they've been around for a billion years.
Evidence reported in Nature on October 1 by scientists in the lab of Whitehead Member and Howard Hughes Medical Institute investigator David Bartel provides a window into the early evolution of these key regulators, placing their origin within the earliest of animal lineages. The research also suggests that microRNAs present early on have undergone extensive changes, which likely have altered their functions across various lineages.

"This is the first evidence that microRNAs were present within the earliest animal lineages and are not just characteristic of more complex animals," says Andrew Grimson, a postdoctoral fellow in Bartel's lab. Scientists knew that microRNAs existed within bilaterians, an evolutionary group that includes everything from worms to fruit flies to humans, he explains. "Remarkably, we discovered their presence within sponge, a member of the earliest diverging group of animals."